Global Warming leads to Underwater Deserts. SUHAS.E.P I Year.Dept of Mechanical engineering RVCE

Transcription

1 Global Warming leads to Underwater Deserts SUHAS.E.P I Year.Dept of Mechanical engineering RVCE

2 Introduction Oxygen-poor waters occupy large volumes of the intermediate-depth eastern tropical oceans. Oxygen-poor conditions have far-reaching impacts on ecosystems because important mobile macro organisms avoid or cannot survive in hypoxic zones. Climate models predict declines in oceanic dissolved oxygen produced by global warming. Scientists constructed 50-year time series of dissolved-oxygen concentration for select tropical oceanic regions by augmenting a historical database with recent measurements. These time series reveal vertical expansion of the intermediate-depth low-oxygen zones in the eastern tropical Atlantic and the equatorial Pacific during the past 50 years. The oxygen decrease in the 300- to 700-m layer is 0.09 to 0.34 micro moles per kilogram per year. Reduced oxygen levels may have dramatic consequences for ecosystems and coastal economies.

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4 Climatological mean dissolved oxygen concentration at 400 m depth using ocean data software:

5 Oceanic dissolved oxygen concentrations have varied widely in the geologic past. For instance, paleoclimate records from the Cretaceous reveal profoundly altered biogeochemical cycles and dramatic consequences associated with reductions of ocean oxygen. The anoxic ocean at the end of the Permian (251 million years ago) is perhaps the most striking example, being associated with elevated atmospheric CO 2 and massive terrestrial and oceanic extinctions. The global ocean has warmed substantially over the past 50 years and strong inter annual-todecade variations of oxygen have been observed in the upper 100 m. Long-term oxygen changes have been observed and reported in the sub polar and subtropical regions. For instance, in the subtropics Pacific at Ocean Station Papa (50 o N, 145 o W), declining oxygen concentrations have been reported from depths of 100 to 400 m between 1956 and Ocean oxygen data from the most oxygen-poor tropical regions of the OMZ are limited, but some regions exist for which historical date can be augmented with date from recent survey programs to construct relatively long quasi-continuous oxygen time series

6 The tropical ocean OMZs in the central and eastern tropical Atlantic and equatorial pacific oceans appear to have expanded and intensified during the past 50 years. Despite the sparseness of observations, the time series used show, that the decline in oxygen content has been most intense in the tropical Atlantic, where at present, hypoxic regions are small as compared with the Pacific and Indian Oceans. For these reasons, the Atlantic may also have the most potential for large increase in the area of hypoxic regions. The observations analysis presented here supports climate model predictions of dissolved oxygen declines in the tropical ocean and an expansion of the tropical OMZs due to a contribution of thermal, dynamical, and biogeochemical factors. The observed oxygen declines reported here of 0.09 to 0.34 µmol /kg a year for 300- to 700- m depths are somewhat smaller than those reported in the North Pacific at 100 to 400 m. Together, these trends affect carbon and nitrogen cycles, with fundamental implications for marine ecosystems and thereby fisheries resource management issues. Given climate model projections, and the geological record that indicates times of widely distributed suboxic regions, sustained global ocean measurements of dissolved oxygen concentrations are needed (for instance, by equipping more Argo floats with well-calibrated dissolved oxygen sensors), to more closely monitor variations in the strength and extent of the

7 GLOBAL WARMING AND COASTAL DEADZONES The Gulf of Mexico dead zone, extending west on the inner Louisiana Texas, continental shelf from the mouth of the Mississippi river, is perhaps the most famous. It has developed virtually every summer since the early 1970 s and can cover 22,000sqkm The deep hypoxic zone of the Baltic Sea is even larger and has become a year round, multi decade feature. Seasonal dead zones are prominent in the Chesapeake Bay, long island sound, many smaller us bay estuaries, and in coastal environments around the world, particularly in Europe and Asia. Some 169 of these hypoxic zones are increasing. Although natural process can cause and contribute in the development of hypoxia and anoxia, most of these dead zones have developed or been exacerbated by human activities, particularly in the increasing of loading of nutrients nitrogen and phosphorous on various forms from land to the coastal waters.

8 Dissolved oxygen concentrations plummet in bottom waters, killing animals or requiring them to flee if fish, crustaceans and shellfish are taken by predators as they live the relative safety of their bottom habitats. Biogeochemical changes enhance the return of nitrogen and phosphorous from sediments to the water column, refueling the fire of primary production of vicious cycle. As a result, the important ecosystems these coastal environments provide are compromised. Reports on how climate change may already be influencing oxygen availability in the ocean, unrelated to nutrient loading from the human activities, underscores the sensitivity of ocean life to this great 21 st century challenge. Changes in the wind patterns have resulted in the shifts in ocean currents and deep upwelling causing hypoxia and mass mortalities in recent years along the inner shelf off Oregon and Washington coasts deep oxygen minimum zones tropical oceans vertically increased over the last 50 years.

9 The way forward Future projections and current warning signs of the effects of global warming should provide a sense of urgency in our efforts to abate coastal eutrophication resuscitate dead zones. Healthy, resilient ecosystems will still be subject to change, but will allow better for better adaptation and management options. Restoring the wetlands within the watersheds of these coastal ecosystems and managing coastal wetlands in a ways that enhance their ability to build soils and migrate inland as sea level rises would preserve Or enhance their capacity as a sink of nutrients. Also In the coming decades, if not years, there will enormous pressure to find ways to reduce greenhouse gas emissions. There are pathways that could produce ancillary benefits in terms of reducing coastal dead zones (for example, carbon capture and sequestration from power plants could also eliminate nitrogen oxide emissions). In any case it is now time to take climate change into account in our efforts to reduce coastal dead zones and to consider fully the collateral effects, including dead zones, in our efforts to slow global warming.

10 THANK YOU